1. Field of the Invention
The present invention relates to telecommunications, and, in particular, to the allocation of bandwidth resources in a cellular system.
2. Description of the Related Art
A conventional cellular telephone system comprises a number of cell sites or base stations, geographically distributed to support transmission and receipt of voice-based communication signals to and from cellular telephones, often referred to as mobiles, although any given cellular telephone may actually be stationary. Each cell site handles voice communications over a particular region called a cell, and the overall coverage area for the cellular telephone system is defined by the union of cells for all of the cell sites, where the coverage areas for nearby cell sites overlap to some degree to ensure (if possible) contiguous communications coverage within the outer boundaries of the system""s coverage area. One cell site may sometimes provide coverage for several sectors. In this specification, cells and sectors are referred to interchangeably.
When active, a mobile receives forward-link signals from and transmits reverse-link signals to (at least) one cell site. Each active mobile is assigned a forward-link channel on which it receives its forward-link signals and a reverse-link channel on which it transmits its reverse-link signals. There are many different schemes for defining channels for a cellular telephone system, including TDMA (time-division multiple access), FDMA (frequency-division multiple access), and CDMA (code-division multiple access) schemes. In CDMA communications, different channels are distinguished by different spreading sequences that are used to encode different voice-based streams, which may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver can recover a, particular voice-based stream from a received signal using the appropriate spreading sequence to decode the received signal.
In order to avoid interference between signals transmitted to and from mobiles in a cellular telephone system, all active mobiles within a particular cell are assigned different CDMA spreading sequences. Since cellular telephone systems are dynamic systems in which mobiles become active and inactive at different (and possibly random) times and since mobiles can move from one cell to another, the assignment of channels to the various mobiles is made by the cellular system in real time. In order to assign bandwidth resources to mobiles so as to avoid interference between mobiles in neighboring cells, the resource-assignment activities of neighboring cell sites may have to be coordinated.
In conventional cellular telephone systems, each mobile transmits and receives only voice-based communication signals. As such, each active mobile requires the assignment of only a single forward-link channel and a single reverse-link channel, where each channel in the system has the same fixed amount of bandwidth. For example, in the IS-95 family of CDMA-based communication standards, each channel in a system is either 9.6 kbps or 14.4 kbps, depending on which of two rate sets is implemented.
Future cellular telecommunication systems, however, such as those conforming to the IS-95B standard or wideband CDMA standards, such as the CDMA2000 and the WCDMA standards, or TDMA Packet Data standards currently being developed, will support mobiles that transmit and receive signals other than just voice-based signals. For example, a mobile data terminal may be designed to transmit and/or receive data streams. Such mobiles may require more bandwidth than is available in a single CDMA channel. Moreover, unlike voice-based streams, which are typically continuous streams with fairly uniform bit rates, data streams are typically bursty streams consisting of packets of data transmitted intermittently. As such, the bandwidth requirements for a mobile transmitting and/or receiving data (as opposed to voice only) will vary over time. The conventional schemes for assigning individual channels to mobiles for the durations of their active periods will typically not satisfy the requirements of a cellular telecommunication system that supports the transmission and receipt of bursts of data to and from mobiles.
The present invention is directed to a scheme for assigning additional bandwidth in a cellular telecommunication system that supports the transmission and receipt of bursts of data to and from mobiles. Such a scheme may be referred to as a burst admission control scheme, since it controls the admission of bursts to or from mobiles currently supported by a cell site for data transmission.
Depending on the system, the additional bandwidth may take different forms, such as one or more supplemental channels or a single channel having a variable bandwidth. In general, in this application, unless otherwise clear from the context, whenever one or more supplemental channels are referred to, it will be understood to refer to systems that can allocate multiple supplemental channels as well as systems that allocate variable bandwidth of a single channel.
The IS-95B standard, for example, provides the air-interface messaging structure to provide high data rate service. Similar procedures and messages are being written into data standards for TDMA and wideband CDMA. Efficient burst admission control schemes and procedures are needed to operate the service utilizing these messages and to optimize the spectral and network resource usage. The burst admission control schemes of the present invention take into account the following components: (i) procedures to estimate the available radio resources based on the measurements by the mobile and the cell site, and (ii) procedures to allocate the available resources to multiple data users accounting for fairness and efficiency.
In one embodiment, the present invention is a method for assigning additional bandwidth in a cellular telecommunication system, comprising the steps of (a) receiving an initial request for assignment of additional bandwidth for a user and determining whether to grant or reject the initial request, such that, if the initial request is rejected, instructions are given to submit a retry request after a back-off time; (b) receiving a continuation request for reassignment of additional bandwidth for an ongoing burst and determining whether to grant or reject the continuation request, such that, if the continuation request is rejected, instructions are given to submit a retry request after a back-off time; and (c) receiving a retry request for assignment of additional bandwidth after a previous request was rejected and determining whether to grant or reject the retry request, such that, if the retry request is rejected, instructions are given to submit a retry request after a back-off time.